Periostin levels are unlikely to have been influenced by the presence or absence of atopy in either the asthma or non-asthma group [12, 13], but It is possible that serum periostin levels may show a greater magnitude of circadian variability in a population in which there is a greater proportion with uncontrolled disease, similar to an effect shown with FeNO [21]. Here, POSTN is linked to asthma.